The additive manufacturing process is widely known as “3D printing.” Numerous 3D-printing methodologies have been described in prior art, the most common being selective-laser sintering (SLS), stereolithography (SLA), and extrusion-based 3D printing or fused filament fabrication (FFF).
In FFF, a 3D object is produced, in accordance with a mathematical model thereof, by extruding a succession of small, flattened strands of molten material that harden as soon as they leave the extrusion nozzle. The object is built from the bottom up, one layer at a time.
In SLS, a laser selectively fuses powdered material by scanning, on the surface of a powder bed, cross-sections generated from a 3-D digital description of the object. After scanning a cross-section, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the object is completed.
In stereolithography, an ultraviolet (UV) laser is directed toward a vat of photopolymer resin. Using computer aided design software (CAM/CAD), the UV laser draws a design or shape on the surface of the photopolymer vat. Due to its photosensitivity to UV light, the resin solidifies and forms a single layer of the nascent 3D object. This process is repeated for each layer of the design until the 3D object is complete.
Although suitable for prototyping, most 3D printed objects are typically not robust enough to be used as structural parts, such as for use in automotive, aerospace, medical or other aggressive-use applications. This is the case regardless of the methodology (FFF, SLS, SLA) used.
The excellent mechanical properties of carbon nanotubes (“CNTs”) and graphene suggest that incorporation of a very small amount of either of these materials into a polymer matrix can lead to structural materials having exceedingly high durability and high strength as well as low weight. To date, however, the production of high-strength CNT polymer composites has proven to be rather difficult; CNT-infused polymers produced thus far show some improvement in strength, but far below expectations.
Research has indicated that poor adhesion between the polymer and CNT is the limiting factor for imparting the mechanical properties of CNTs to polymer composites. Moreover, van der Waals interactions cause CNTs to form stabilized bundles, making them very difficult to disperse and align in a polymer matrix.
Researchers have focused on ways to effectively disperse CNTs into a polymer matrix. Thus far, techniques that have found at least some success for dispersing CNTs in the polymer matrix include: solution mixing, melt mixing, electrospinning, in-situ polymerization, and chemical functionalization of the CNTs.
Although 3D-printed objects have been made using CNT/polymer composites, the resulting parts do not demonstrate any significant enhancement in mechanical properties (c.a., no more than about a three-fold increase, which in the context of CNTs for example, is negligible compared to the potential). Rather, CNT/polymer-composite printed objects are currently being used for their electrical properties, such as to control electrostatic discharge.